(i) Technical Field
A certain aspect of the embodiments discussed herein is related to a method for fabricating a semiconductor device. Another aspect of the embodiments is related to a method for fabricating a semiconductor device in which a GaN-based semiconductor layer is formed on a silicon substrate.
(ii) Related Art
Semiconductor devices using a gallium nitride (GaN) based semiconductor are used as a power device operating at high frequencies and outputting high power, and a light emitting diode or a laser diode emitting light of short wavelengths. Particularly, there has been considerable activity in the development of semiconductor devices suitable for amplification in a high-frequency or RF (radio Frequency) band such as a microwave band, a quasi-millimeter band or a millimeter band. Examples of those semiconductor devices are an FET such as a high electron mobility transistor (HEMT) and light emitting devices such as a laser diode (LD) and a light emitting diode (LED).
Generally, a sapphire substrate or a silicon carbide (SiC) substrate is used as a substrate on which the GaN-based semiconductor layer is grown. Since the sapphire substrate and the SiC substrate are expensive, there has been developed an art of growing the GaN-based semiconductor layer on the silicon (Si) substrate. As Si and Ga react easily, an AlN layer is interposed between the Si substrate and the GaN-based semiconductor layer as a barrier layer (see Japanese Patent Application Publication No. 2008-166349).
However, a pit-like defect may occur on the surface of the AlN on the Si substrate. In case where the GaN-based semiconductor layer is formed on the AlN layer on which many pit-like defects occur in order to form a HEMT, for example, a process for fabricating the transistor may be affected. For example, electrodes may not be formed reliably. Another problem is a deterioration of the crystal quality of the GaN-based semiconductor layer, which leads to a degradation of the transistor characteristics.